In the continuing search for polymers suitable for use at elevated temperatures, many different repeating structures involving diverse connecting linkages have been suggested, e.g., aromatic structures connected by linkages such as imides, ethers, sulfones, ketones, etc. Unfortunately, as performance at elevated temperature has been enhanced, the amenability of the candidate polymers to classical molten techniques of polymer fabrication has declined. Generally, a decline in melt processability also accompanies attempts to produce high temperature resistant polymers having a room temperature elongation of at least about 50%, a necessary property for many polymer applications, e.g., if a wire insulated with the polymer is to be capable of being twisted about itself without cracking of the insulation.
Aromatic polyketones are known to enjoy good resistance to thermal degradation. Bonner, in U.S. Pat. No. 3,065,205, suggests the Friedel-Crafts catalyzed polymerization of certain reactants to yield polyketones. The reactants proposed fall into two classes, aromatic diethers and polynuclear aromatic hydrocarbons, either of which are reacted with aliphatic or aromatic diacyl chlorides. The basic reactions taught by the Bonner patent can be summarized as follows: EQU (1) n(HR--O--RH)+n(Cl--A--Cl).fwdarw.(2n-1)HCl+H(R--O--R--A).sub.n Cl
and EQU (2) n(HBH)+n(Cl--A--Cl).fwdarw.(2n-1)HCl+Cl(A--B).sub.n H
where HBH is a polynuclear aromatic hydrocarbon such as naphthalene, HR--O--RH is an aromatic ether such as diphenyl ether, and Cl--A--Cl is an aromatic or aliphatic chloride such as terephthaloyl chloride or phosgene. When phosgene and diphenyl ether are reacted, for example, the resulting polymer will contain the repeating unit ##STR4##
An entirely different approach to aromatic polyketones is taken by Farnham and Johnson in British Pat. No. 1,078,234. Here, polyarylene polyethers are produced by reaction of an alkali metal double salt of a dihydric phenol with a dihalo benzenoid compound. The dihydric phenol may contain a keto group--thus, 4,4'-dihydroxy benzophenone is claimed to be polymerizable with 4,4'-dichlorobenzophenone to afford a polyketone of the structure ##STR5##
The same polymer repeating unit is disclosed in British Pat. No. 971,227 to arise from the reaction of diphenyl ether with phosgene, from the polycondensation of diphenyl ether-4-carbonyl chloride, and from the reaction of diphenyl ether with diphenyl ether-4,4'-dicarbonyl chloride.
A number of patents dealing with improved methods of making polyketones have issued. Thus, for example, processes disclosed in U.S. Pat. Nos. 3,441,538 and 3,442,857 derive advantage by resort to hydrogen fluoride-enhanced boron trifluoride catalysis, a catalyst system described in Boron Fluoride and Its Compounds as Catalysts, etc. by Topchiev et al., Pergamon Press (1959), p. 122; J. Org. Chem. 26 2401 (1961); and I&E Chem. 43,746 (1951). A further patent dealing with an improved polymerization process is British Pat. No. 1,086,021.
Example 10 of British Pat. No. 971,227 describes a process for preparing the polymer of repeating unit ##STR6## The reported product showed no signs of flowing on heating up to 350.degree. C. and apparently required spinning from solution for fiber formation. The product is also variously described, in Example 1 of U.S. Pat. No. 3,441,538, as yielding polymer of low elongation which afforded opaque brown films, while in British Pat. No. 1,153,527, this polymer is characterized as highly crystalline and intractable from the stand-point of conventional melt fabrication.
The teaching of the foregoing references are incorporated herein by reference to illuminate the background of this invention. It is thus apparent that previous attempts to synthesize polymer I have afforded material of at best questionable purity and/or structural uniformity, e.g., freedom from branching. The prior art, e.g., U.S. Pat. Nos. 3,674,627; 3,637,592, the disclosures of which are incorporated herein by reference, also teach the preparation of other aromatic polysulfones and/or polyketones.
In all instances, isolation and purification of these aforementioned polymers has always presented great difficulties both because of their inherently relatively intractable nature, especially when crystalline, and the intractable nature of most of the preferred polymerization media (e.g., hydrofluoric acid/boron trifluoride). I have, in contradistinction, found that readily melt processable polymers of the above types can be formed if certain synthesis and work-up procedures, as hereinafter described, are utilized. The hereinafter described work-up procedures are also applicable to the synthesis of numerous other polymers. In particular, I have found that aromatic polyketones and aromatic polysulfones produced by Friedel-Crafts catalysed polymerization, as hereinafter described in greater detail, are of substantially enhanced melt processability and thermal and oxidative stability in comparison with analogous polymers produced using prior art Friedel-Crafts polymerization methods.
In U.S. Pat. No. 3,441,538, mentioned hereinabove, it is suggested that polymer I be precipitated by pouring the above-mentioned reaction mixture into methanol, then dissolved in dichlorotetrafluoroacetone hydrate, the solution filtered and the polymer reprecipitated by pouring the solution into methanol. Another isolation technique suggested in the same patent include extracting the polymer, initially precipitated as above, exhaustively with boiling methanol, followed by acetone and dioxane. A similar technique to this last described is also disclosed in U.S. Pat. No. 3,442,857: in one example the crude polymer (precipitated by pouring the reaction mixture into methanol) is leached with boiling pyridine or aqueous ammonia solution. These above techniques are also disclosed in Berr, U.S. Pat. No. 3,516,966.
U.S. Pat. No. 3,668,057 to Angelo discloses the preparation and purification of larger amounts of aromatic polyketone to be used in the extrusion of film. The polymerization reaction mixture (hydrogen fluoride/boron trifluoride) is poured into aqueous ammonia to precipitate the polymer and the precipitated polymer washed with N,N'-dimethylacetamide, then four times with water, thrice with methanol, and dried under vacuum at 50.degree. C. for 2 days. The polyketone was then redissolved in dichloroacetic acid and four very small aliquots of triethylsilane reducing agent were added. The solution was left to stand for several hours, then one last aliquot of triethyl-silane added, the solution poured into a mixture of distilled water and the precipitated polymer washed again successively with N,N'-dimethylacetamide, water and methanol as before. As is apparent, as incredibly complex purification procedure was deemed essential to provide a product of acceptable quality.
Gander et al, in U.S. Pat. No. 3,791,890 refers to the difficulties caused by the "relatively intractable nature of the initial polymer catalyst complex upon formation" (using an HF/BF.sub.3 catalyst reaction media) and discloses a method for spraying the reaction mixture into a dispersing medium (liquid or gaseous) such as air, preferably at a temperature between 70.degree. and 120.degree. C., to facilitate preparation of a polyketone such as I in a granular form.
Also, in my U.S. Pat. No. 3,953,400, and in my U.S. Pat. No. 3,751,398, I disclose that dilution of the polyketone polymerization mixture with from 10 to 90% liquid sulfur dioxide (based on the hydrogen fluoride) reduces the stability of the boron trifluoride hydrogen fluoride ketone complex (possibly by reducing the polarity of the solution) and facilitates removal of solvent and catalyst during spray-drying. However, this process suffers from certain disadvantages For example, because it depends on dilution for its effect, substantially complete removal of catalyst only occurs at high dilutions. Thus, the solids content of the mixture to be sprayed must be very low, most preferably below 1 percent. The viscosity of the polymer solution in sulfur dioxide/hydrogen fluoride mixtures is much higher than in hydrogen fluoride alone, and this presents an upper limit to the solids content for solutions to be sprayed which is also undesirably low. Thus, a need has existed for a method of effecting isolation of polyketones and polysulfones which produces the polymer in a clean and melt-stable form and does not suffer from any of the disadvantages of heretofore known processes as set forth above.
It is an object of this invention to provide aromatic polyether ketones and polyether sulfones which are substantially uncontaminated by catalyst residues, especially in the form of complexes with the polymer, or other contaminants.
It is another object of this invention to overcome the relatively intractable nature of the initial polymer catalyst complex thereby rendering these polymers amenable to separation from the reaction mixture.
It is another object of the invention to provide facile, inexpensive and reliable isolation techniques for working up aromatic polyketone and polysulfone polymerization mixtures.
All these and other objects and advantages of the instant invention will be further discussed or made apparent in conjunction with the detailed description thereof and of the embodiments and examples thereof set forth hereinafter.